Solar cycle 24

Solar Cycle 24 was the most recent solar cycle, the 24th since 1755, when extensive recording of solar sunspot activity began.[1][2] It began in December 2008 with a smoothed minimum sunspot number of 2.2.[3] Activity was minimal until early 2010.[4][5] It reached its maximum in April 2014 with a 23 months smoothed sunspot number of 81.8.[6] This maximum value was substantially lower than other recent solar cycles, down to a level which had not been seen since cycles 12 to 15 (1878-1923).

Solar cycle 24
ISES Solar Cycle 24 Sunspot Number Progression
Sunspot data
Start dateDecember 2008
End dateMay 2020
Max count81.8
Max count monthApril 2014
Min count2.2
Spotless days489
Cycle chronology
Previous cycleSolar cycle 23 (1996-2008)
Next cycleSolar cycle 25 (2019-~2030)
NASA Solar Cycle 24 Sunspot Number Prediction

Reversed polarity polar active sunspot regions in December 2016, April 2018, November 2018, May 2019, and July 2019 indicate that a transitional phase to solar cycle 25 is in process.[7][8]

Predictions

Prior to the minimum between the end of Solar Cycle 23 and the beginning of Solar Cycle 24, two theories predicted how strong Solar Cycle 24 would be. One camp postulated that the Sun retained a long memory (Solar Cycle 24 would be active) while the other asserted that it had a short memory (quiet). Prior to 2006, the difference was substantial with a minority of researchers predicting "the smallest solar cycle in 100 years."[9] Another group of researchers, including one at NASA, predicted that it "looks like its going to be one of the most intense cycles since record-keeping began almost 400 years ago."[10]

The delayed onset of high latitude spots indicating the start of Solar Cycle 24 led the "active cycle" researchers to revise their predictions downward and the consensus by 2007 was split 5-4 in favor of a smaller cycle.[11] By 2012, consensus was a small cycle, as solar cycles are much more predictable 3 years after minima.

In May 2009 the NOAA Space Weather Prediction Center's Solar Cycle 24 Prediction Panel predicted the cycle to peak at 90 sunspots in May 2013.[12] In May 2012 NASA's expert David Hathaway predicted a peak in Spring of 2013 with about 60 sunspots.[13]

NASA funded and used Ken Schatten's physics-based models,[14] which utilized a solar Dynamo model, to accurately predict the low. This method used the correlation between solar magnetic field strength at solar minimum to sunspot number at solar maximum to accurately predict the peak solar flux of each of the last three solar cycles. Schatten's predictions become accurate as early as solar minima, 5–6 years before solar max.

Results

In early 2013, after several months of calm, it was obvious that the active 2011 was not a prelude to a widely predicted late 2012-early 2013 peak in solar flares, sunspots and other activity. This unexpected stage prompted some scientists to propose a "double-peaked" solar maximum, which then occurred. The first peak reached 99 in 2011 and the second peak came in early 2014 at 101.[15]

Speculation
The 2008 breach of Earth's magnetic shield

According to NASA, the intensity of geomagnetic storms during Solar Cycle 24 may be elevated in some areas where the Earth's magnetic field is weaker than expected. This fact was discovered by the THEMIS spacecraft in 2008.[16][17] A 20-fold increase in particle counts that penetrate the Earth's magnetic field may be expected.[18] Solar Cycle 24 has been the subject of various hypotheses and commentary pertaining to its potential effects on Earth.

While acknowledging that the next solar maximum will not necessarily produce unusual geomagnetic activity, astrophysicist Michio Kaku took advantage of the media focus on the 2012 phenomenon to draw attention to the need to develop strategies for coping with the terrestrial damage that such an event could inflict. He asserted that governments should ensure the integrity of electrical infrastructure, so as to prevent a recurrence of disruption akin to that caused by the solar storm of 1859.[19]

The current solar cycle is currently the subject of research, as it is not generating sunspots in the expected manner. Sunspots did not begin to appear immediately after the last minimum (in 2008) and although they started to reappear in late 2009, they were at significantly lower rates than anticipated.[20]

On April 19, 2012, the National Astronomical Observatory of Japan predicted that the Sun's magnetic field would assume a quadrupole configuration.[21]

Throughout 2012, NASA posted news releases discrediting the 2012 phenomenon and the so-called Mayan prophecy, delinking them from solar activity and space weather.[22][23]

Events
Solar flares by year
10
20
30
40
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
  •   M5-M9
  •   X1-X5
  •   X5-X9
The strongest flares of Solar Cycle 24 (above M5.0 class) and related events
ClassYearDateSunspot regionRadio B.SR StormCMEGM Storm
X9.332017Sep 62673R3S1Yes-
X8.22017Sep 102673R3S3Yes-
X6.92011Aug 91263R3S1Yes-
X5.42012Mar 71429R3S3YesG3
X4.92014Feb 251990R3S1YesG2
X3.32013Nov 51890R3-Yes-
X3.22013May 141748R3-Yes-
X3.192014Oct 242192R3-No-
X2.82013May 131748R3-Yes-
X2.742015May 52339R3-Yes-
X2.32013Oct 291875R3-Yes-
X2.22011Feb 151158R3-YesG1
X2.22014Jun 102087R3-?-
X2.22015Mar 112297R3-Yes-
X2.22017Sep 62673R3-?-
X2.12013Oct 251882R3-Yes-
X2.12011Sep 61283R3S1YesG3
X2.02014Oct 262192R3-No-
X2.02014Oct 272192R3-No-
X1.92011Nov 31339R3-Yes-
X1.92011Sep 241302R3S1YesG4
X1.82011Sep 71283R3S1YesG1
X1.82012Oct 231598R3-No-
X1.82014Dec 202242R3-Yes-
X1.72013Oct 251882R3-Yes-
X1.72012Jan 271402R3S2Yes-
X1.72013May 131748R3-Yes-
X1.662014Sep 102158R3S2YesG3
X1.62014Oct 222192R3-No-
X1.52011Mar 91166R3-YesG2
X1.52014Jun 102087R3-?-
X1.42011Sep 221302R3-Yes-
X1.42012Jul 121520R3S1YesG2
X1.32012Mar 71430R3S3No-
X1.32014Apr 252035R3-?-
X1.32017Sep 72673R3S2NoG4
X1.22014Jan 71944R3S2Yes-
X1.22013May 151748R3S1YesG1
X1.12012Mar 51429R3-YesG2
X1.12012Jul 61515R3S1YesG1
X1.12013Nov 81890R3-Yes-
X1.12013Nov 101890R3-Yes-
X1.12014Oct 192192R3-No-
X1.02013Nov 191893R3S1Yes-
X1.02013Oct 281875R3S1Yes-
X1.02014Mar 292017R3-?-
X1.02014Jun 112087R3-?-
X1.02014Oct 252192R3-No-
M9.92014Jan 11936R2-Yes-
M9.32013Oct 241877R2-Yes-
M9.32011Aug 41261R2S1YesG4
M9.32011Jul 301260R2-No-
M9.32014Mar 121996R2-?-
M9.22015Mar 72339R2-Yes-
M9.02012Oct 201598R2-Yes-
M8.72012Jan 231402R2S3YesG1
M8.72014Oct 222192R2-No-
M8.72014Dec 172242R2-Yes-
M8.42012Mar 101429R2-Yes-
M8.32010Feb 121046R2-Yes-
M8.22015Mar 32290R2-Yes-
M8.12017Sep 82673R2-?-
M7.92012Mar 131429R2S2YesG2
M7.92014Nov 52205R2-Yes-
M7.92015Jun 252371R2S1YesG2
M7.72012Jul 191520R2-Yes-
M7.62015Sep 282422R2-?-
M7.62016Jul 232567R2-Yes-
M7.42011Sep 251302R2-YesG1
M7.32014Apr 182036R2S1?-
M7.32014Oct 22173R2-Yes-
M7.32017Sep 72673R2-?-
M7.22014Jan 71944R2-No-
M7.12011Sep 241302R2-YesG4
M7.12014Oct 272192R2-?-
M6.92012Jul 81515R2S1Yes-
M6.92014Dec 182241R2-Yes
M6.72011Sep 81283R2-YesG1
M6.72014Oct 272192R2-?-
M6.72016Apr 182529R2-Yes-
M6.62011Feb 131158R2-Yes-
M6.62011Feb 181158R2-No-
M6.62014Jan 301967R2-Yes-
M6.62014Oct 282192R2-?-
M6.62015Jun 222371R2S2YesG4
M6.52013Apr 111719R2S2Yes-
M6.52014Apr 22027R2-?-
M6.52014Jul 82113R2-?-
M6.52014Nov 32205R2S1Yes-
M6.42010Feb 71045R2-Yes-
M6.42013Dec 311936R2-Yes-
M6.32013Nov 11884R2-Yes-
M6.32012Mar 91429R2-YesG2
M6.12012Jul 51515R2-No-
M6.12012Jul 281532R2-Yes-
M6.12014Dec 42222R2-Yes-
M6.02012Nov 131613R2-Yes-
M6.02011Aug 31261R2-YesG4
M5.92013Jun 71762R2-Yes-
M5.92014Aug 242151R2-?-
M5.82011Sep 241302R2-?-
M5.82015Mar 92297R2-Yes-
M5.72012May 101476R2-Yes-
M5.72013May 31739R2-Yes-
M5.72014Nov 162209R2-?-
M5.72017Apr 22644R2-No-
M5.62012Jul 21515R2-Yes-
M5.62015Jan 132257R2-No-
M5.62015Aug 242403R2-?-
M5.52012Aug 181548R2-No-
M5.52015Oct 22422R2-?-
M5.52016Jul 232567R2-Yes-
M5.52017Sep 42673R2-?-
M5.42010Nov 61121R2-?-
M5.42014Nov 62205R2-?-
M5.32011Sep 61283R2-YesG3
M5.32011Mar 81165R2-YesG1
M5.32012Jul 41515R2-Yes-
M5.32014May 82056R2-?G1
M5.32017Apr 22644R2-No-
M5.22014Feb 41967R2-?-
M5.12012May 171476R2S2Yes-
M5.12013Oct 281875R2-Yes-
M5.12014Sep 282173R2-Yes-
M5.12015Mar 102297R2-Yes-
Source: Solarham.com[24] and NOAA's SWPC.[25] The CME field indicates whether the solar flare hurled a CME (oriented or not to Earth). The Radio B./SR Storm/GM Storm fields indicate the NOAA scales of radio blackouts/solar radiation storms/geomagnetic storms, being G1 (minor), G2 (moderate), G3 (strong), G4 (severe) and G5 (extreme).

2008

On January 4, 2008, a reversed-polarity sunspot appeared, presaging the arrival of Solar Cycle 24 -- though not marking its official beginning. It was high latitude (30° N) and magnetically reversed. NOAA named the spot AR10981, or sunspot 981 for short.[4]
Sunspot 1007 produced the first solar flare above the B-class on November 2, 2008.
Sunspot 1009 produced the first solar flare above the C-class, a C1.4, on December 11, 2008. Only a few sunspots were observed on the surface of the Sun throughout 2008. The smoothed monthly sunspot number reached a minimum in December 2008 (2.2), therefore an international panel of scientists declared that month as the beginning of Solar Cycle 24. [26]

2009

Solar activity remained extremely low throughout 2009. The observed monthly sunspots exceeded 10 only in December.

2010

January

Sunspot 1041 produced the first solar flare above the M-class, an M2.3 (followed by an M1.7 just seven hours after and by four consecutive M flares, the strongest reaching M3.4, the next day) on January 19, 2010.

February

Sunspot 1046 produced an M8.3-class flare on February 12, 2010. 9 M-class flares were unleashed by active regions 1045 and 1046 this month.

April

On April 5, 2010 the first coronal mass ejection (CME) of Solar Cycle 24 produced by a sunspot (but unrelated to flares; in fact, a single C-class X-ray flux event was registered this month) and causing a true geomagnetic storm was registered. The Kp index, which quantifies disturbances in the horizontal component of Earth's magnetic field, was 7 by then, so the geomagnetic storm reached a G3 (strong level) on the NOAA G-scale.

August
Multiple coronal mass ejections

On August 1–2, 2010, scientists at the Harvard-Smithsonian Center for Astrophysics (CfA) observed a series of four large CMEs emanating from the Earth-facing hemisphere by analyzing images recorded at NASA's Solar Dynamics Observatory. They were expected to reach the Earth's geomagnetic field sometime between August 4 and early August 5. As of 05:00 UTC August 4, the estimated time of arrival of the series was as follows:

  • Wednesday, August 4 – 07:00 UTC
  • Wednesday, August 4 – 17:00 UTC
  • Thursday, August 5 – 00:00 UTC
  • Thursday, August 5 – 06:00 UTC[27]

All four ejections were described as large and, according to scientists, possessed enough energy to cause aurorae to be observed by the naked eye in non-polar regions.[28] According to reports, aurorae would be visible at night toward the poleward horizon in temperate latitudes between 45° to 50°, and near overhead in regions closer to the poles.[29] The initial coronal mass ejection of August 1 originated from a sunspot designated Sunspot 1092, which was large enough to be seen without the aid of a solar telescope.[30] Aside from the visual effects of this CME series, scientists warned that electric impulses caused by disruptions in the magnetic field due to the ionized particles may damage infrastructure such as power grids and telephone lines not adequately protected against induced magnetic current. It had also been reported that several Earth-orbiting satellites might have been in similar danger.[28] According to Leon Golub, an astronomer at CfA:

This eruption is directed right at us and is expected to get here early in the day on August 4. It's the first major Earth-directed eruption in quite some time. When such an expulsion reaches Earth, it interacts with the planet's magnetic field and can create a geomagnetic storm. Solar particles stream down the field lines toward Earth's poles. Those particles crash with atoms of nitrogen and oxygen in the atmosphere, which then glow like little neon signs. Sky watchers in the northern U.S. and other countries should look toward the north late Tuesday or early Wednesday for rippling "curtains" of green and red light.[31]

Solar flare

According to the Solar Dynamics Observatory, these CMEs were probably connected to a C3.2-class solar flare that peaked on August 1 at 08:26 UT. The origin of this blast was sunspot 1092. The connection between both events was established despite the ~400,000 km distance between them.[32]

Aurorae observations

In the early morning hours of August 4, 2010, aurorae occurred in the northern hemisphere that were visible at latitudes as far south as Michigan and Wisconsin in the United States, and Ontario, Canada near latitude 45° North. European observers reported sightings as far south as Denmark near latitude 56° North. The aurorae were reportedly green in color due to the interaction of the solar particles with oxygen atoms in the relatively denser atmosphere of southern latitudes.[33] This, however, was only the first wave of solar wind; the third and last was expected for the evening of August 5,[34] but missed Earth entirely. The geomagnetic storm reached a G2 (moderate) level on the NOAA scale.

Solar radiation storm

Unrelated to the multiple coronal mass ejections, some days after, on August 14, a C4.4-class flare produced the first solar radiation storm of Solar Cycle 24. The proton storm event was minor, rating at S1, and was easily absorbed by the ionosphere.

November

Active region 1121 emitted an M5.4 flare on November 6.[35]

December

The year 2010 ended up with 21 M-class solar flares.

2011

February
'Valentine’s Day' 2011 flare

Peaking at 01:56 UT on February 15, 2011, sunspot group 1158 produced an X2.2-class solar flare. Dubbed the Valentine's Day solar event by the scientific community, it was the first Solar Cycle 24 flare reaching X class level. In fact, it was the first of its class since December 2006. NOAA issued an R3 (strong) radio blackout alert pertaining this prominent x-ray flux event. In addition to flashing Earth with X and UV radiation, the explosion also hurled a CME in Earth's direction. The magnetosphere was impacted on February 18. The CME struck a minor G1-level geomagnetic storm.[36][37]
Shortly before, on February 13, sunspot 1158 had unleashed an M6.6-class solar flare. On February 18, the same active region produced another x-ray burst with the same strength.[38] 13 M-class bursts were registered in February 2011.

March

A CME exploded from the vicinity of sunspot 1164 during the late hours of March 7, 2011. It leapt away from the Sun traveling ~2200 km/s, making it the fastest CME since September 2005.
On March 9, active region 1166 erupted in an X1.5 flare. An R3-level radio blackout was reported. The related CME caused a G2 geomagnetic storm two days later.[39] 21 M-class flares were registered this month.

July

Sunspot 1260 produced an M9.3-class solar flare on July 30, 2011. Because of its brevity, the eruption did not hurl a substantial cloud of ionized material or CME toward Earth, so it was not geoeffective.[40]

The Aug 9, 2011 X6.9-class flare, taken by NASA's Solar Dynamics Observatory (SDO) in extreme UV light at 131 Angstroms.
The active region 1302, responsible for two X-class flares in Sep 22 and 24, 2011. Image taken that month by NASA's SDO.

August

On August 5, 2011, the combined cloud of three consecutive CMEs produced brilliant aurorae, reported as far south as Oklahoma and Alabama. The geomagnetic storm reached a G4 (severe) level, enough to create power outages. It was one of the strongest geomagnetic storms in years. In the southern hemisphere, aurorae could be seen as far north as South Africa, Southern Chile and Southern Australia. The CMEs were hurled by three M-class flares erupting in active sunspot 1261: M1.4 on August 2, M6.0 on August 3 and M9.3 on August 4.[41][42][43]

X6.9-class flare

On August 9 at 08:05 UT, sunspot 1263 produced a massive X6.9-class solar flare, the third X-flare of Solar Cycle 24 and the most powerful so far (as of May 2013). There was also a CME associated with this burst. Although the flare was not Earth-directed, radiation created waves of ionization in Earth's upper atmosphere, briefly disrupting communications at some VLF and HF radio frequencies. An R3-level (strong) radio blackout alert was issued. A proton event greater than 10 MeV (million electron volts) and exceeding 10 pfu (proton flux units) was also reported, so an S1-level solar radiation storm was also issued.[44]

September

Sunspot 1283 erupted with an M5.3-class solar flare on September 6 at 01:50 UT. An R2 (moderate) blackout radio alert was issued. The burst was Earth-directed. Just 21 hours later, an X2.1-class flare – some four times stronger than the earlier flare – erupted from the same sunspot region. NOAA detected an R3 (strong) radio blackout and an S1 (minor) solar radiation storm. The combined CMEs of these bursts arrived at Earth on September 9, provoking a G3 (strong) geomagnetic storm.

The next day, September 7, an X1.8-class solar flare erupted from sunspot 1283, producing an S1 solar radiation storm. A fourth flare, an M6-class, was ejected by the same sunspot on September 8.[45][46][47]

This sequence of flares produced waves of ionization in Earth's upper atmosphere, briefly altering the propagation of low-frequency radio signals around Earth. Moreover, the eruptions hurled clouds of plasma in its direction. CME impacts, strong geomagnetic storms and aurorae were registered from September 9 onwards.

Then, on September 22, an X1.4-class solar flare erupted out of sunspot 1302. An R3-level radio blackout was registered. The blast produced a significant CME, but was not Earth directed. Two days later, an X1.9-class flare, followed in the next 31 hours by a spectacular string of 14 M-class flares, the biggest being two M7 flares, was mostly unleashed out of the same sunspot. The first two explosions, X1.9 and M7.1, propelled a pair of closely spaced CMEs. A G4 (severe) geomagnetic storm was reported on September 26.[48][49]

In total, the Sun produced four X flares and 31 M flares in September 2011, one of the most active months of Solar Cycle 24 so far.

October

The Sun unleashed eight M-class flares this month, being the strongest the M3.9 event, followed by an Earth-directed CME, produced by sunspot 1305 on October 2. Just in the eve, sunspots 1302 and 1305 had emitted flares almost at the same time; the first event was a C-class and the second one reached a M1.2 category. This double eruption, which hurled a double CME as well, were particularly interesting as coincided with the arrival of a comet, discovered by amateur astronomers the previous day, that disintegrated in spectacular fashion when it plunged into the Sun. A very similar scenario happened on May 10–11, 2011.[50]

November

On November 3, 2011, active region 1339, one of the largest sunspots in years - 40,000 km wide and at least twice that in length - unleashed an X1.9-class solar flare. Waves of ionization in the upper atmosphere created an R3 (strong) radio blackout. The related CME was not headed for Earth.[51] 13 M-class flares were registered this month. November 2011 may be considered the most active month of the current Cycle 24 so far, as monthly sunspot count was nearly 100 (96.7) and the same went for the F10.7 Solar Flux (the radio emission from the Sun at a wavelength of 10.7 cm) that racked up a value of 153.1. However, these numbers are well below those of Cycle 23 at its peak. Cycle 23 peak sunspot count was 170 and its F10.7 was about 235.[52]

December

Solar activity increased again in late December, with the Sun unleashing eight M-flares. The most intense flare, produced by sunspot 1385, was an M4.0 event on December 25.[53] The year 2011 ended up with 111 M-class and 8 X-class solar flares.[54]

2012

January

Active sunspot 1401 erupted an M3.2-class solar flare and a full-halo CME on January 19, 2012. The CME hit the Earth's magnetic field in the early hours of January 22, with minor geomagnetic disturbances reported.[55]
Sunspot 1402 erupted a long-duration M8.7-class flare, followed by a CME, on January 23, 2012 at 03:59 UTC. According to NOAA, the flare's radiation storm was ranked as S3 (strong), the strongest since May 2005.[56] The very fast-moving CME arrived at the Earth on January 24 at approximately 15:00 UTC. The geomagnetic storm reached a G1 level (minor), the same level recorded by the previous M3-class flare.[57]

SOHO view of the Jan 23, 2012 M8.7 flare.
SDO shot of the Jan 23, 2012 M8.7 flare.
SDO shot of the Jan 23, 2012 M8.7 flare.
The M3.2 class solar flare of 19 January 2012, by SDO.

On January 27, at 18:37 UT, sunspot region 1402 unleashed an X1.7-class flare, prompting NOAA's Space Weather Prediction Center to issue an R3 (strong) Radio Blackout warning and an S2 (moderate) Solar Radiation Storm warning. Sunspot 1402 was rotating onto the far side of the Sun, so the blast site was not facing Earth. The explosion also produced a huge CME, but not Earth-oriented, so no geomagnetic storm was expected.[58][59]

March

Following several minor C-class flares, M-class flares and CMEs registered in previous days and weeks, active region 1429 erupted an X1.1-class flare on March 5 at 04:13 GMT. The wave of high energy electromagnetic rays, reaching Earth in minutes, caused an R3 (strong) radio blackout over China, India and Australia, according to NOAA. Sunspot region 1429, whose size was half of that of Jupiter and was rotating toward Earth, was being particularly active since it materialized on March 2. The CME that followed arrived at the Earth on March 7 and caused a G2 (moderate) geomagnetic storm. Just hours after ejecting the X1.1-class flare, it produced several minor C and M-class flares in quick succession.[60][61]

X5.4-class flare

After releasing up to nine M-class flares in only one day, the active region 1429 erupted a powerful X5.4-class flare at 00:24 UTC on March 7. The related CME impacted the Earth on March 8, causing a G3 (strong) geomagnetic storm. This event marked the second strongest solar flare of Cycle 24 in terms of X-ray flux. NOAA launched R3 (strong) radio blackout and S3 (strong) solar radiation storm alerts.[62] Just one hour after that first flare, nearby sunspot 1430 released a less powerful X1.3-class flare. No CME associated to this event was reported.[63] Months later, in June, NASA reported that its Fermi Gamma-ray Space Telescope detected in this powerful flare the highest flux of gamma rays — greater than 100 MeV — ever associated with an eruption on the Sun.[64]

AR1429, rotating toward the other side of the Sun, generated an M6.3-class flare on March 9, an M8.5 flare one day later and an M7.9 flare on March 13. These eruptions hurled CMEs, all Earth-oriented. The first wave of plasma impacted the magnetosphere on March 12, causing a G2 (moderate) geomagnetic storm. The second CME was not geoeffective. The third wave of ionized gas reached Earth on March 15, causing another G2 storm.

In late March, the US Air Force Space Command reported that the solar storms of March 7–10 could have temporarily knocked American military satellites offline.[65] NASA also reported that these powerful flares heated the Earth's upper atmosphere with the biggest dose of infrared radiation since 2005. From March 8 to March 10, the thermosphere absorbed 26 billion kWh of energy. Infrared radiation from carbon dioxide and nitric oxide, the two most efficient coolants in the thermosphere, re-radiated 95% of that total back into space.[66]

March 2012, one of the most active months of Solar Cycle 24, ended up with 19 M-class and three X-class flares.

April

A prominent eruption produced a CME off the east limb (left side) of the Sun on April 16, 2012.[67] Such eruptions are often associated with solar flares, and in this case an M1.7-class (medium-sized) flare occurred at the same time, peaking at 1:45 PM EDT (17.45 UTC).[67] The CME was not aimed toward Earth.[67] Nevertheless, this month was very quiet in comparison to the previous one, as only two M-class flares were recorded.

May

Solar activity increased again this month, with 12 M-class flares ejected, the strongest being an M5.7 flare produced by active region 1476 on May 10. This so-called "monster" sunspot complex, the largest active region of the cycle to date, was about the size of Jupiter, or eleven times the diameter of Earth.[68]

June

11 M-class solar flares were observed this month, the largest being an M3.3 flare.

July

An X1.1-class flare erupted from sunspot 1515 on July 6, generating an R3 (strong) radio blackout and an S1 (minor) solar storm; its related CME caused a G1 (minor) geomagnetic storm. Six days after, sunspot 1520, the largest active region of Solar Cycle 24 to date, unleashed an X1.4-class flare, peaking at 12:52 PM EDT. This huge group of sunspots, which rotated into view on July 6, was located in the center of the Sun at the time of this event. The related CME caused a G2 (moderate) geomagnetic storm, following an R3 radio blackout and an S1 solar storm.[69]

Video of the July 12, 2012 X1.4 flare using SDO AIA footage in 131(teal), 171(gold) and 335 (blue) angstrom wavelengths.
The formation of the flux rope (lower right limb) that preceded the July 19, 2012 M7.7 flare.
The July 19, 2012 M7.7 flare.

The Sun emitted a moderate solar flare on July 19, 2012, beginning at 1:13 AM EDT and peaking at 1:58 AM. The flare was classified as an M7.7 flare. It was also emitted from sunspot 1520.[70] Other M-class flares registered this month included an M6.9 (July 8, sunspot 1515), an M6.1 (July 5, sunspot 1515), an M6.1 (July 28, sunspot 1532), an M5.6 (July 2, sunspot 1515) and an M5.3 (July 4, sunspot 1515). The month ended up with 45 M-class flares and 2 X-class flares, which is the highest number of such flares within the current solar cycle to date. Nevertheless, July 2012 was not the most active month in solar radio flux and number of sunspots.

Solar storm of 2012
Main article: Solar storm of 2012
August 31, 2012 CME: pictured here is a lighten blended version of the 304 and 171 angstrom wavelengths.

August

On August 31, 2012, a long filament of solar material that had been hovering in the Sun's atmosphere (the corona) erupted out into space at 4:36 p.m. EDT.[71] The CME traveled at over 1500 km (900 miles) per second. The CME did not travel directly toward Earth, but did connect with Earth's magnetic environment, or magnetosphere, with a glancing blow. causing aurorae to appear on the night of Monday, September 3.[71] A G2 (moderate) geomagnetic storm was registered on September 3 and September 5.[72] The Sun erupted 10 M-class flares this month, the largest being an M5.5 burst ejected on August 18.

September

A filament eruption occurred during the late hours of September 27, resulting in a brief S1 (minor) radiation storm, alerted by NOAA in the early hours of the next day. The Earth-directed CME associated with this event affected Earth on September 30. A G3 geomagnetic storm was registered on October 1. The filament eruption was connected to a C3.7 flare which occurred in the vicinity of sunspot 1577.[73] Solar activity decreased remarkably this month. 4 minor solar flares, below M2, were registered in September 2012.

October

On October 8 and 9, the arrival of a CME unrelated to solar flares and emitted on October 5 caused disturbances in the horizontal component of the Earth's magnetic field. The planetary Kp-index reached level 6, so a G2 (moderate) geomagnetic storm was reported.[74] The Sun released an M9.0 flare on October 20. This was followed three days later on October 23 by a very impulsive flare, peaking as an X1.8-class event at 3:17 a.m. UTC.[75][76] Both flares came from active region 1598, located on the left side (east) of the sun, which had previously been the source of a number of weaker flares. The M9.0 burst occurred when the sunspot was not yet rotated onto the Earth-facing side of the solar disk.[75] The NOAA categorized the radio blackout associated with the X1.8 event as an R3.[75] This was the 7th and last X-class flare in 2012.[75] There was no associated Earth-directed CME.[75]

November

14 M-class flares were registered this month, the strongest being an M6.0 flare, which erupted on November 13 by AR1613.[77]

December

Solar activity decreased significantly this month. For first time in two years (since December 2010), no X or M-class flares were emitted by the Sun's Earth-facing side (the strongest flare was merely a C4.1). The observed sunspots were 40.8 and the 10.7 cm radio flux value was 108.4, the lowest in ten months.[78]

2012 ended up with 129 M-class and 7 X-class solar flares.[54]

2013

April
The 13–15 May 2013 series of four X-class flares erupted by AR1748: X1.7, X2.8, X3.2 and X1.2. Shots taken by NASA's Solar Dynamics Observatory (SDO) in the 131 Angstrom wavelength of extreme UV light.
The 13–15 May 2013 series of four X-class flares as they were registered by the real-time monitor of GOES satellites X-ray Flux (NOAA/SWPC).

The unexpectedly low solar activity continued in April 2013. Only 13 M-class flares were reported from December 2012 to April 2013, the strongest being an M6.5 unleashed by active region 1719 on the 11th. This event generated an R2 radio blackout and an R2 radiation storm. The observed sunspots this month were 72.4 and the 10.7 cm radio flux value was 125.0.[78][79]

May
String of X-class flares

Solar activity increased rapidly in mid-May 2013 with four consecutive strong flares in two days. These powerful bursts all surged from the just-numbered sunspot AR1748, located on the eastern limb of the Sun and barely rotating around the front of the solar disk. AR1748 emitted the first flare, an X1.7-class, on May 13, peaking at 02:17 UTC. This event was quickly followed the same day at 16:09 UTC by an X2.8-class flare. On May 14 at 01:17 UTC the same sunspot emitted an X3.2-class flare, the third strongest of the current solar cycle so far. This was followed by an X1.2-class flare at 01:52 UTC on May 15. The four X-ray bursts generated an R3 (strong) radio blackout in the upper atmosphere.

Every X-ray event was followed by a CME. The first three CMEs were not geoeffective at all as they were not directed toward Earth; the fourth CME was partially geoeffective, so a G1 (minor) geomagnetic storm was expected to occur on May 18. An S1 (minor) proton storm event was also detected in connection with the May 15 X1.2 flare.[80]

2014

February

On February 24, 2014, the sun erupted with an X4.9-class solar flare, the strongest of that year.[81]

October

Four solar flares occurred within 5 days from sunspot AR 12192, which is both the largest sunspot of solar cycle 24 and the largest since 1990. On October 19 there was a major X1.1-class solar flare. On October 22 an M8.7-class flare was followed by an X1.6 event. The October 24 X3.1-class solar flare was strong enough to trigger a radio blackout. Larger than the planet Jupiter, the AR 12192 sunspot was visible during a partial solar eclipse seen in North America.[81]

2015

June
The SDO captured an image of the June 25, 2015 event.

The sun emitted a mid-level solar flare, an M7.9-class, peaking at 4:16 a.m. EDT on June 25, 2015.[82]

November

In early November 2015, solar flares disrupted the air traffic control system in central and southern Sweden, causing heavy delays for passengers.[83]

2016

December

A sunspot group originally attributed to the new solar cycle 25 is observed.[84] The sunspot numbers continue to decline.

During 2016, there were 26 days with no sunspots (preliminary numbers).[85]

2017

March

As of 31 March, preliminary reports indicate there had been 24 days during 2017 during which there were no sunspots.[85]

September

On 6 September the largest X-class flare in a decade (X9.3) erupted from active region 2673.[86][87] Then, when this region was just crossing the west limb, another X-class flare (SOL2017-09-10, X8.2) produced only the second ground-level particle event of the cycle.[88] Sunspot region 2673 was one of the most active regions during the entire cycle, creating both of the largest flares in the cycle and 4 total X-class flares. No further M class flares would take place during the rest of Solar cycle 24.

2018

January

A small active region, NOAA 12694, appeared at the surprisingly high latitude of S32, near the disk center (January 8). Its location conflicted directly with the expectation from the butterfly diagram. In principle new-cycle spots should appear at such a latitude, but this region had the correct polarity for Cycle 24.

March

NOAA reported that the number of sunspots was the lowest since 2009, and that recent activity matched that of the low activity in 2007 and 2008. Should this prove to be the solar minimum, Solar Cycle 24 would uniquely become a short (10 year) and weak cycle. Sunspots were observed on only 5 days that month.

2019

May

A C6.8 flare took place on 9 May 2019, the strongest solar flare to take place since October 2017.[89]

July

NASA's Solar Dynamics Observatory recorded a sunspot from Solar Cycle 25. This sunspot is significant compared to previous sunspots from Solar Cycle 25 due to the fact that it lasted long enough to get a designation.[90]

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See also

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